[Bug target/90204] [8/9 Regression] C code is optimized worse than C++

[crazylht at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90204

--- Comment #3 from Hongtao.liu <crazylht at gmail dot com> ---
(In reply to Hongtao.liu from comment #2)
> It seems such code generation is r254855's intention.
> 
>                 /* Use 256-bit AVX instructions instead of 512-bit AVX
> instructions
> 4695                in the auto-vectorizer.  */
> 4696             if (ix86_tune_features[X86_TUNE_AVX256_OPTIMAL]
> 4697                 && !(opts_set->x_ix86_target_flags &
> OPTION_MASK_PREFER_AVX256))
> 4698               opts->x_ix86_target_flags |= OPTION_MASK_PREFER_AVX256;
> 
> I know there is a frequency reduction issue when many zmm registers are
> used, but i don't know what exact situation did r254855 deal with?

But it should generate assemble like what g++ did which also use ymm instead of
zmm.